Current methods of emergency fluid resuscitation in the pre-hospital setting are inadequate due to the large volumes required of convention resuscitation solutions. Recent research by us and other suggest that exceedingly small volumes of highly hperosmotic formulation can safely and rapidly restore blood pressure, cardiac output and oxygen consumption after moderate hemorrhage. The overall goal of the proposed research is to better understand the physiological mechanisms of action of small volume hypertonic resuscitation. Towards this goal we will measure the integrated cardiopulmonary response to infusion of hypertonic fluids in normovolemic and hypovolemic animals. Specific Aims are: 1) to measure the cardiac function before and after hypertonic infusions in normovolemic and hemorrhaged animals. direct and indirect effects of hypertonic saline will be evaluated for the augmentation of cardiovascular performance after hypertonic resuscitation. 2) to better understand the rapid natriuresis/diuresis observed after hypertonic resuscitation. We will sequentially evaluate if the natriuresis is induced through atria natriuretic peptide or the intrarenal production of postaglandins and brandykinins. 3) to provide consultant and analytical support to ongoing and planned clinical trials of 7.5 NaCl/6% dextran 70 for resuscitation of trauma. We will measure the integrated cardiovascular response in a dynamic hemorrhage model designed to mimic the clinical setting.